The present invention relates to a lug wrench (sometimes known as a wheel brace) for the tightening and loosening of wheel nuts on vehicles of various kinds.
It is sometimes necessary to change a wheel and replace with a spare, for example, due to a puncture of the tire, or, other wheel/tire damage. In practice, it is often difficult to loosen the wheel nuts, due to previous over-tightening, and/or, slight corrosion between the nuts and their associated studs.
It is customary for a lug wrench to be supplied, with the vehicle, by the manufacturer of the latter. However, to prevent over-tightening of the wheel nuts and to allow compact storage of the lug wrench, the latter is normally relatively short in length, thus typically requiring a significant amount of strength to be applied to loosen the wheel nuts.
To overcome the latter problem, one type of commercially available lug wrench (sometimes known as an extending lug wrench) comprises an outer tube, which slides over an inner bar having a square drive for a socket head at the wheel nut end. The product is capable of providing additional leverage for the loosening of wheel nuts by extending the outer tube away from the wheel nut axis. When tightening the wheel nuts, the extending lug wrench is intended to be utilized in the retracted mode to avoid over-tightening, which is likely to result in future wheel nut removal problems and, in extreme cases, could damage the threads on the wheel studs and/or nuts. However, utilization in this way relies entirely on the user taking care to fully retract the lug wrench outer tube prior to wheel nut tightening.
There is various prior art which addresses the problem of preventing wheel nuts being over-tightened due to the application of an excessive tightening torque by the user. For example, EP 0086082 discloses a form of torque limiting ratchet to prevent over-tightening of nuts, with the lug wrench embodiment described having a mechanical advantage provided by the use of gearing. The ratchet disclosed comprises a pair of discs, each having a series of ramps, arranged face-to-face and loaded together by a spring up to a predetermined limit. The embodiment described involves the use of epicyclic gearing requiring external constraint (on the wheel rim) of one of the ring gears and cage and thus requires means to engage another wheel nut or the wheel rim. The need for a torque limiting ratchet, the use of epicyclic gearing and the requirement for external constraint make the lug wrench relatively costly to produce and complicated to use.